Effects of external potassium supply on compartmentation and flux characteristics of radiocaesium in intact spring wheat roots

lShort term experiments investigated the effects of potassium supply on radiocaesium influx/efflux and the radiocaesium compartmentation in intact spring wheat roots. Short term (24-72 h) influx analysis showed that net influxes of radiocaesium to both root and xylem were reduced approximately ten-times by increasing external potassium concentration from 50 mu M to 200 mu M. Efflux analysis distinguished three components for radiocaesium (namely cell wall + free space, cytoplasm and vacuole) and showed that the rates of Cs+ efflux at an external potassium concentration of 100 mu M (19.16 and 1.70 Bq g(-1) min(-1) for (co) and (vo), respectively) were about three-times faster than those at 50 mu M (7.24 and to 0.41 Bq g(-1) min(-1) for (co) and (vo), respectively). The results also showed that external potassium concentration did not have a significant effect on the distribution of Cs-137 between cytoplasm and vacuole, as indicated by the ratio of Cs-137 in the two compartments. Results obtained in this study suggested that the inhibitory effect of potassium on the net uptake of radiocaesium by the plant root may be partially ascribed to the fact that at higher external potassium concentrations Cs+ efflux rates were much higher. The mechanisms involved are discussed. (C) 1999 Annals of Botany Company.